One of the primary objects of the present invention is to alter the well known disadvantageous engineering characteristics of plastic clay soils and subgrade soils. The problems encountered in highly plastic soils and subgrade soils are well known to those skilled in the art.
It is also well known that hydrated lime as a common additive may be used to reduce the plasticity index and increase the load carrying capacity of clay soils.
However, quite often the chemical reaction of lime, when processed with water and mixed into the clay soil results in the lime forming calcium carbonate instead of the beneficial calcium hydroxide. This is caused by the inherent presence of carbon dioxide in the air which is supplied to the soil during the intimate mixing of the lime therewith. Also, the benefits of lime to improve the load bearing characteristics of plastic clays are substantially reduced if not completely eliminated, by the amount of lime reacting with the carbon dioxide to form calcium carbonate. Further, even if all the lime reacted to form the calcium hydroxide and thus reduce the plasticity index while increasing the load carrying capacity, such reaction is delayed over an undesirable period of time.
Also, it is well known that portland cement will also decrease the plasticity index and increase the load bearing characteristics thereof in about the same degree as lime as well as producing a rapid higher strength gain in a friable soil. However, since one to five days of "mellowing" time is required to make the plastic soil friable, most of the strength gained characteristics of cement are lost because of the delay required to reduce the plasticity index. For example, when the cement is mixed with the soil, the moisture present in the soil initiates hydration of the cement. On the other hand, as stated above the one to five day mellowing period, preferably about three days, is provided to allow the lime which is released from the portland cement to react with the soil thereby reducing its plasticity and making it friable. Then, after the plastic soil becomes friable, it is remixed and shaped to the desired grade and compacted.
It can be appreciated that such remixing to permit the intimate contact of the soil particles with the additive to enable bonding of the particles in order to increase the load carrying capacity when the mixture is compacted destroys the increased loading carrying capacity of the soil due to the cement during the mellowing period.
Also, it is known to employ 2 to 3 weight percent of hydrated lime to make a plastic soil friable, then 3 to 5 weight percent portland cement after the "mellowing" period to produce the desired increase in load carrying capacity. Although the end results are consistent because the portland cement does not lose its value by forming the useless calcium carbonate, as does the lime, the added cost of spreading the cement has made this method seldom used.
An object of the present invention is to enable a filler and portland cement to be mixed together and used as the additive to reduce the plasticity index of a plastic soil and provide a resulting strengthened soil matrix. To accomplish this, a suitable filler is employed with the portland cement mixture as well as a retarding agent to delay the action of the portland cement.
A still further object of the invention is to provide a composition including cement, a filler and retardant, with the cement or the retarder in a form to permit the clay soil to first become friable before hydration of the cement is initiated.
A still further object of the invention is to provide a composition including portland cement, a filler and retardant, with the cement in a form to permit the clay soil to first become friable before hydration of the cement is initiated.
A still further object of the invention is to provide a composition including portland cement, a filler and retardant, with the retarder in a form to permit the clay soil to first become friable before the hydration of the cement is initiated.
Yet another object of the present invention is to provide a composition including portland cement, a filler and pellets of retardant coated with different thicknesses of a water soluble coating which releases the retardant in a required dosage over a period of time to permit the clay soil to become friable.
Still another object of the present invention is to provide a composition and method of its use wherein the filler and portland cement mixture is provided with a retardant all in liquid form.
Yet another object of the invention is to provide a method of reducing the plasticity of a soil and provide the desired resulting strengthened soil matrix by adding a mixture to the soil of portland cement, a retarder, and a filler.